Battery blowing voltage regulators "why"

Or like when I got a string of 3 bad DieHards from the same Sears store. I finally 'connected the dots' that all of them had a 2 marks spaced apart the same distance in the sides of the opaque plastic cases..... like the plastic had been compressed. All of them were in a batch that musta been knocked against something in shipping or handling somewhere along the line, and probably had cracked/broken plates causing the symptoms of internal shorts. (One shorted itself while sitting overnight, over heated, burned to top off and leaked acid all inside the trunk of my 1st race car!)